In mining operations, it is necessary as a safety precaution to stabilize or shore up mine roofs to reduce the likelihood of their collapse. To this end, roof plates or boards are bolted to the mine roof to prevent pieces of rock from falling down and injuring miners or sealing off passageways. In the process of installing a roof bolt plate, a bolt hole is drilled in the mine roof and a generally rectangular plate or board is affixed to the roof by a mechanical bolt or a bolt grouted in place by means of a resin bolting system.
A number of roof bolting drills are found in the prior art for drilling bolt holes in preparation for installing a roof bolting plate. The roof bolting drill is provided with a drill head which is movable mechanically in a vertical direction. Attached to the drill head is a chuck having a relatively shallow female end which is rotated at high speed by the drill head. Lengths of hollow tubular drill steel drivers are usually connected to the chuck during a drilling operation. In the prior art, a number of different drill steel drivers are employed during a single drilling operation. More specifically, to drill a bolt hole to a depth of six feet, a drill steel starter having a relatively short lower male end is mounted onto the female end of the chuck, and an oversized bit is connected to the upper female end of the starter drill steel. The drill head rotates the starter and bit thereby initiating the drilling operation. The drill head is mechanically raised until the hole is drilled to a depth equal to the length of the drill steel starter driver. The drill head is then lowered such that the drill steel starter and the oversized drill bit may be entirely removed from the hole, enabling the starter and bit to be disconnected from the chuck. A lead extension driver having a relatively deep female end, which is connected to a second drill bit having a smaller diameter, is then inserted into the partially drilled bolt hole. The second bit must be of a lesser diameter than the first bit to facilitate the insertion of the bit into the hole. A second lower drill steel driver having a relatively short male lower end is then inserted into the chuck and its relatively deep upper female end is connected to the lead extension. Drilling is resumed with the drive head raising the lower driver and lead extension up into the bolt hole. Should the combination of the lead extension and the lower drill steel driver fail to drill a hole to the desired depth, the lower driver is disconnected from the lead extension and lowered such that a middle extension driver can be installed between the lower driver and the lead extension. A conventional middle extension driver is provided with a relatively long lower male end and a relatively deep upper female end. By repeated additions of middle extension drivers, drilling may continue until a hole is drilled to the desired depth.
Thus, each time a bolt hole was drilled in a mine roof using known systems, two different drill bits were required in addition to the use of a variety of drivers such as the starter, lead extension, lower driver and middle extension. Further, the chuck employed in the prior art has a fairly shallow female upper end which results in potentially dangerous procedures. More specifically, when the drill steel drivers are retracted from the bolt hole, they are generally rotated to facilitate withdrawal. Frequently, the bit or a portion fo the drill steel will become jammed in the bolt hole causing the unwanted and sudden separation of the drill steel from the chuck such that the free end of the drill steel creates a hazard to the operator. Further, if the drill steel accidentally breaks, the portion of the drill steel which remained in the chuck tends to fly out, which can also result in injury to the operator.
Therefore, it is an object of the subject invention to provide an apparatus and a method for drilling a bolt hole in a mine roof wherein the drill steel drivers utilized in the drilling operation are substantially identical.
It is another object of the subject invention to provide an apparatus and a method for drilling bolt holes in a mine roof wherein only one size drill bit need be used in each drilling operation.
It is a further object of the subject invention to provide an apparatus and a method for drilling holes in a mine roof wherein the roof bolting drill is provided with a chuck having a female drive of extended depth thereby providing uniform, straight drill holes, and improved safety for the operator.
It is still another object of the subject invention to provide a method and apparatus for drilling a hole in a mine roof which is faster and more economical then heretofore.